Processes for producing nano-space controlled polymer ion-exchange membranes

Abstract

A polymer film substrate is irradiated with ions to make a large number of nano-sized through-holes and the substrate may be further irradiated with ionizing radiation so that a functional monomer may be grafted or co-grafted onto a surface of the film and within the holes; in addition, sulfonic acid group(s) may be introduced into the graft chains to produce a polymer ion-exchange membrane that may have high oxidation resistance, dimensional stability, electrical conductivity and/or methanol resistance, as well as may have an ion-exchange capacity controlled over a wide range.

1. A process for producing a polymer ion-exchange membrane comprising:
 irradiating a first surface of a polymer film substrate with an ion beam selected from the group consisting of hydrogen ions, helium ions or high-energy heavy ions at 10 4 ˜10 14 /cm 2  for forming holes in the substrate; 
 then adding to the irradiated film substrate at least one monomer selected from monomers having a sulfonyl halide group CF 2 ═CF(SO 2 X 1 ), CH 2 ═CF(SO 2 X 1 ) and CF 2 ═CF(OCH 2 (CF 2 ) 1-4 SO 2 X 1 ), wherein X 1  is a halide group —F or —Cl; 
 degassing the monomer or monomers; 
 heating the film substrate so that the monomer or monomers are grafted onto the substrate; 
 converting the halide group —X 1  in grafted molecular chains to the sulfonate group —SO 3 M, where M is an alkali metal Na or K; and then 
 converting the sulfonate group to the sulfonic acid group —SO 3 H. 
 
     
     
       2. The process for producing a polymer ion-exchange membrane according to  claim 1 , wherein at least one acrylic comonomer selected from CF 2 ═CR 2 (COOR 3 ) is added for graft polymerization in an amount no more than 50 mol % of total monomer content, where R 2  is —CH 3  or —F, and R 3  is —H, —CH 3 , —C 2 H 5  or —C(CH 3 ) 3 . 
     
     
       3. The process for producing a polymer ion-exchange membrane according to  claim 2 , wherein the polymer film substrate has a second surface opposite the first surface,
 wherein for the first surface irradiated with the ions, and each of the ions has a range not greater than a film thickness, and 
 wherein the second surface is irradiated with a varying dose of similar or dissimilar ions having a range not greater than the film thickness, such that the two ranges will overlap in a bulk of the film. 
 
     
     
       4. The process for producing a polymer ion-exchange membrane according to  claim 3 , wherein the polymer film substrate is selected from polyethylene terephthalate, super-high-molecular weight polyethylene, polypropylene, polystyrene, polyamide, aromatic polyamide, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyetherketone, polyetheretherketone, polyethersulfone, poly(phenylene sulfide) or polysulfone film substrate. 
     
     
       5. The process for producing a polymer ion-exchange membrane according to  claim 3 , wherein the polymer film substrate is selected from polyimide, polyetherimide, polyamideimide, polybenzimidazole or polyetheretherimide film substrate. 
     
     
       6. The process for producing a polymer ion-exchange membrane according to  claim 3 , wherein the polymer film substrate is selected from poly(vinylidene fluoride), ethylene-tetrafluoroethylene copolymer, polytetrafluoroethylene, tetrafluoroethylene-propylene hexafluoride copolymer or tetrafluoroethylene-per(fluoroalkyl)vinyl ether copolymer film substrate. 
     
     
       7. The process for producing a polymer ion-exchange membrane according to  claim 1 , wherein the polymer film substrate has a crosslinked structure. 
     
     
       8. The process according to any one of  claims 1 - 7 , wherein at least one crosslinking agent is selected from divinylbenzene, bis(vinylphenyl)ethane, triallyl cyanurate, triallyl isocyanurate, 3,5-bis(triflourovinyl)phenol or 3,5-bis(trifluorovinyloxy)phenol and the crosslinking agent is added for graft polymerization in an amount no greater than 30 mol % of total monomer content. 
     
     
       9. The process according to any one of  claims 1 - 7 , wherein a degree of grafting is 10-120% and an ion-exchange capacity is 0.3-2.5 meq/g. 
     
     
       10. The process according to any one of  claims 1 - 7 , wherein irradiating is followed by applying ionizing radiation selected from X-rays, γ-rays or electron beams.